<?php 

  include('wp-load.php');

  $nike = get_term_by('slug','nike','brand'); // This here just to illustrate

  $terms = get_cross_referenced_terms(array(
    'post_type'        => 'product',
    'related_taxonomy' => 'brand',
    'term_id'          => $nike->term_id,
  ));
  foreach($terms as $term) {
    echo "<p>{$term->name}</p>";
  }

function get_cross_referenced_terms($args) {
  global $wpdb;
  $args = wp_parse_args($args,array(
    'post_type'        => 'post',
    'taxonomy'         => 'category',
    'related_taxonomy' => 'post_tag',
    'term_id'          => 0,
  ));
  extract($args);
  $sql = <<<SQL
SELECT DISTINCT
  {$wpdb->terms}.*,
  COUNT(*) AS post_count
FROM
  {$wpdb->terms}
  INNER JOIN {$wpdb->term_taxonomy} ON {$wpdb->terms}.term_id={$wpdb->term_taxonomy}.term_id
  INNER JOIN {$wpdb->term_relationships} ON {$wpdb->term_taxonomy}.term_taxonomy_id={$wpdb->term_relationships}.term_taxonomy_id
  INNER JOIN {$wpdb->posts} ON {$wpdb->term_relationships}.object_id={$wpdb->posts}.ID
  INNER JOIN {$wpdb->term_relationships} related_relationship ON {$wpdb->posts}.ID=related_relationship.object_id
  INNER JOIN {$wpdb->term_taxonomy} related_term_taxonomy ON related_relationship.term_taxonomy_id=related_term_taxonomy.term_taxonomy_id
  INNER JOIN {$wpdb->terms} related_terms ON related_term_taxonomy.term_id=related_terms.term_id
WHERE 1=1
  AND (related_term_taxonomy.taxonomy<>{$wpdb->term_taxonomy}.taxonomy OR related_terms.term_id<>{$wpdb->terms}.term_id)
  AND {$wpdb->posts}.post_type='%s'
  AND {$wpdb->term_taxonomy}.taxonomy='%s'
  AND related_term_taxonomy.taxonomy='%s'
  AND related_terms.term_id=%d
GROUP BY
  {$wpdb->terms}.term_id
SQL;
  $sql = $wpdb->prepare($sql,$post_type,$taxonomy,$related_taxonomy,$term_id);
  $terms = $wpdb->get_results($sql);
  return $terms;
}

http://wordpress.stackexchange.com/a/11005

Get all custom taxonomies that are attached to posts that have another custom taxonomy. Like fetching all categories that are attached to products that have the brand taxonomy "Nike".

Get all custom taxonomies that are attached to posts that have another custom taxonomy

wordpress

PHP